Gravity is a force pulling together all matter. The more matter, the more gravity, so things that have a lot of matter such as planets and moons and stars pull with more strength. Mass is how we measure the amount of matter something has in it. The more massive an object is, the more of a gravitational pull it exerts. "As we walk on the surface of the Earth, it pulls on us, and we pull back. But since the Earth is so much more massive than we are, the pull from us is not strong enough to move the Earth, while the pull from the Earth can make us fall flat on our faces." [1]
Newton's Discovery
Arab Science- A Journey of Innovation
Newton first thought up the idea of gravity when, as legend goes, he was sitting under an apple tree when an apple fell from a branch (onto his head or near to him) and he began to ponder what it was that made that apple fall to the ground. Something had to be pulling it down, and eventually Newtonnamed that force gravity. He proclaimed that gravity effected everything on and near Earth, like the moon, and that is was gravity that kept it orbiting around the planet instead of it being flung out into space. Later, after much thought and research, he declared gravity a universal force, which would mean that absolutely everything in the universe is affected by gravity.[6]
The force of gravity between two objects can be expressed by this equation: F=G(m1m2)/r2
In this equation, the G is the constant of universal gravitation, which is a proportionality constant thathas been calculated to be G=6.673 X 10-11 kg-1m3s-2,while m1m2 are the masses of the two objects, between which the force of gravity is being measured, and the r2 is the radius of the rotation between the two objects squared.
In the Law of Gravitation it says that every object in the universe attracts every other object with a force directed along the line of centers for the two objects that is proportional to the product of their masses and inversely proportional to the square of separation between the two objects. He was not the one to come up with this idea though. He merely went further to say that it was this universal force of gravity that proved Kepler’s laws of “inverse squares law” as a natural consequence. Kepler's “inverse squares law” says that the energy twice as far fro
Image Courtesy of http://hyperphysics.phy.astr.gus.edu/HBASE/forces/isq.html
m the source is spread over four times the area; therefore it’s one-fourth the intensity. Although Newton was a professor of mathematics, he made a lot of contributions to physics. When we came out with his three law’s of motion in his “Principia Mathematic Philosophiae Naturalis” it helped to prove his theory of universal gravitation. He put it together only after Halley had asked him why Halley’s Comet and all the planets circled around the sun in an orbit. After that he scrambled to put together his book which is still thought to be one of the best physics books ever published. The only thing it seems to be missing is energy. But his book was still a major breakthrough for his time period. Who knows, if Halley had never approached him about why the comet kept showing up we might still be wondering why the moon and all the other moons of other planets circle them. Or if Halley had not approached him about why this comet “Halley’s comet” keeps reappearing over and over again throughout time the work would be lost forever.
But to prove his theory of universal gravitation he did not use calculus as one might have suspected. Newton’s proof of universal gravitation, that he published, was proven by intricate properties of ellipses and other cronic sections. The most important find of his was not gravity alone, though, but the fact that it was universal. Although today we’ve come up with calculations for finding the force of gravity on an object. To find this lets use the moon as an example; it is at a distance of R proportional to 1/R2 then acceleration G measured on Earth would correctly predict orbital period T. It is used all the time now to calculate the orbital period of satellites and other things that might be flying through our universe. Though, to find the force of attraction between the two objects you need to use a totally different formula. It’s dependant upon the masses of the objects and inversely proportional to the square root of the distance between the centers. This law only works because we live in a three dimensional worl
Image courtesy of https://www.iop.org/.../images%20400/img_tb_4641.gif
d where the gravity just spreads out getting thinner and thinner the farther you go from the source. If we didn’t live in a three dimensional world this law would not work. Only in 1796 was Newton's theory of universal gravitation able to be test by his countryman Henry Cavendish. He did so by noting the slight twist of a dumbbell suspended by a long thread, when on its weights were attracted the gravity of a heavier object called “torsion balance.” Although it’s not that much different from one experiment devised earlier by Charles Augustin Coulomb from France to measure the distance dependence of magnetic and electric forces. This force is not as strong as the pull of say the sun pulling on the earth, but it was still able to be prove his point. A century later the Hungarian physicist Roland Eotovos was able to improve the accuracy of this devise.
Gravity's Affect on Space-time
Courtesy of Stanford University
Space-time is made up of three spacial demensions, length, width, and height. These three demensions are joined with time and all together this makes up the four-demensional setting of the universe. Massive objects tend to "bend" space-time. This can be compared to the well known example of a bowling ball being placed on a tightly drawn sheet. The result is the bowling ball bending the sheet, kind of like how an object such as the Earth or the Sun bends space-time around themselves. Anything that comes near to the objects tend to fall towards the "valley" of bent space-time. It is also believed that these large objects tend to drag space-time around with them wherever they go. In other words, these massive objects are not only making a depression in space time, but they are also, in a sense, twisting the fabric all around themselves. Einstein was also able to prove that time was, in fact, not absolute. It has the ability to change and warp. With all this in mind, it was no longer an accepted idea to think of space as flat.[4]
Even Light is Effected by Gravity
Though one might think light would be able to escape the affects of gravity, it truely is not able too. Light is also affected by gravity just as everything else in the universe. Just as you might throw a ball into the air it will then lose energy the farther it goes. The same thing happens to light as it travels from its source though Electromagnetic waves do not lose energy by going a slower speed. Electromagnetic waves is the scientific name given to light. It achieves this by changing from say a blue frequency to a red frequency which is lower than blue. It is not that different from the way that sound might be changed from where you hear it. Like when an emergency vehicle passes and the pitch changes relative to the po
On this illustration a light ray through gravity is redshifted
sition of the observer. It is related to as the Doppler affect. Whether or not it is like the Doppler affect, motion has the property to affect electromagnetic waves. But a gravitational field is equal to an accelerated motion. So, when you combine the two, the frequency of the wave traveling through the gravitational field is modified by the Doppler affect so that the field then slows down the equivalent motion. But this is not yet known to be a proven theory. It could also be caused by like relative motion. Also it could be caused by celestial bodies, so just about anything that could be flying around in our universe. The last two things that may cause it could be electromagnetic effects or gravitational redshift. A redshift is just when visible light is emitted or reflected to a place of less energy. So it might not be a fact that gravity affects everything in the universe. Too bad Newton is not around today because he would probably be able to figure it out with all the advancements we have made in technology.
How it was discovered?
How Newton discovered universal gravitation was actually by accident. When he saw that apple fall it is thought he started to wonder that if gravity, as he called it, applies here on earth why shouldn’t it apply to everywhere else. He made this discovery in 1666 when he was only twenty four. That’s a big thing considering all the people of the time where more worried about catching the plague. Although he was enrolled in Cambridge university, at that point in time he was at home to avoid the plague, but that’s most of his greatest discoveries were made. It was almost twenty years later, though, when he finally published his findings on this and many other things, including his three laws. Only when Halley persuaded him did he finally publish his findings in the “Principia Mathematica Philosophiae Naturalis.” It is hard to say where we might be today in our knowledge of physics if he had not been sitting under that apple tree. Some of the other contributions Newton discovered durng this time would be things such as binomial theorem, differential calculus, rector addition, centripetal acceleration, and optics. That’s probably why they made him a professor right off when he finally returned to Cambridge after the plague had lifted.
Black Holes
Theoretical Physics- A New Look at the Structure of Spacetime
Even the best scientists still are not entirely sure what exactly a black hole is. A black holes occurs when a supergiant star dies. The lifespan of these stars are rather short, compard the our Sun, and only last about 10 - 15 millions years because it is burning its nuclear fuel much faster than other stars. When it begins to die the star will swell up, turning red, then collapse in on itself creating a violent explosion, called a supernova, then become either a neutron star or, if its mass is greater than 9 solar masses, it will continue falling in on itself until the suns' matter is concentrated into the very small center point that is a black hole. By many, this center is believed to be smaller than the head of a pin. All that matter condensed into such a small point creates a gravitational pull so strong that not even light is able to escape it, but is instead pulled down into the black hole and trapped. Because black holes can caputure light, they cannot be seen, but scientists have discovered that black holes often have planets of their own orbiting them. Scientists used to believe black holes in space to be a rare thing, but since the discovery of planets orbitting what appeared to be nothing at all they have since discovered many black holes to be the center of their own "dead-solar system?" (haha) :]. By recording the movements of these distant planets going around something they cannot see, but clearly is the source of their motions, they are able to calculate the size of the black hole of which the planets are moving around. This method has now become one out of several different ways to detect the existence of black holes. \Many astronomers are beginning to believe that our own Milky Way Galaxy is filled with billions black holes. They have found that black holes are also sometimes close to other normal, visible stars. While they orbit around each other the black holes will tear gas away from the sun, causing that gas to fall violently into the black hole. This causes a great amount of friction between the gas atoms and in turn heats up the gas near the event horizon to several million degrees. The energy from the heated gases radiate out as X-rays and astronomers have been able to detect that radiation with X-ray telescopes. Scientists have recetly introduced a theory stating that most galexies could in fact have a supermassive black hole at its center. The mass of these giant black holes is thought to be between 1 million and 1 billion solar masses (that's big...). Astronomers suspect that these supermassive black holes formed many billions of years ago from gases that gathered at the centers of galaxies. [2][3][5]
Table of Contents
Newton's Law of Universal Gravitation
What is gravity?
Gravity is a force pulling together all matter. The more matter, the more gravity, so things that have a lot of matter such as planets and moons and stars pull with more strength.Mass is how we measure the amount of matter something has in it. The more massive an object is, the more of a gravitational pull it exerts. "As we walk on the surface of the Earth, it pulls on us, and we pull back. But since the Earth is so much more massive than we are, the pull from us is not strong enough to move the Earth, while the pull from the Earth can make us fall flat on our faces." [1]
Newton's Discovery
Newton first thought up the idea of gravity when, as legend goes, he was sitting under an apple tree when an apple fell from a branch (onto his head or near to him) and he began to ponder what it was that made that apple fall to the ground. Something had to be pulling it down, and eventually Newtonnamed that force gravity. He proclaimed that gravity effected everything on and near Earth, like the moon, and that is was gravity that kept it orbiting around the planet instead of it being flung out into space. Later, after much thought and research, he declared gravity a universal force, which would mean that absolutely everything in the universe is affected by gravity.[6]
The force of gravity between two objects can be expressed by this equation:
F=G(m1m2)/r2
In this equation, the G is the constant of universal gravitation, which is a proportionality constant thathas been calculated to be
G=6.673 X 10-11 kg-1m3s-2,while m1m2 are the masses of the two objects, between which the force of gravity is being measured, and the r2 is the radius of the rotation between the two objects squared.
In the Law of Gravitation it says that every object in the universe attracts every other object with a force directed along the line of centers for the two objects that is proportional to the product of their masses and inversely proportional to the square of separation between the two objects. He was not the one to come up with this idea though. He merely went further to say that it was this universal force of gravity that proved Kepler’s laws of “inverse squares law” as a natural consequence. Kepler's “inverse squares law” says that the energy twice as far fro
But to prove his theory of universal gravitation he did not use calculus as one might have suspected. Newton’s proof of universal gravitation, that he published, was proven by intricate properties of ellipses and other cronic sections. The most important find of his was not gravity alone, though, but the fact that it was universal. Although today we’ve come up with calculations for finding the force of gravity on an object. To find this lets use the moon as an example; it is at a distance of R proportional to 1/R2 then acceleration G measured on Earth would correctly predict orbital period T. It is used all the time now to calculate the orbital period of satellites and other things that might be flying through our universe. Though, to find the force of attraction between the two objects you need to use a totally different formula. It’s dependant upon the masses of the objects and inversely proportional to the square root of the distance between the centers. This law only works because we live in a three dimensional worl
Gravity's Affect on Space-time
Space-time is made up of three spacial demensions, length, width, and height. These three demensions are joined with time and all together this makes up the four-demensional setting of the universe. Massive objects tend to "bend" space-time. This can be compared to the well known example of a bowling ball being placed on a tightly drawn sheet. The result is the bowling ball bending the sheet, kind of like how an object such as the Earth or the Sun bends space-time around themselves. Anything that comes near to the objects tend to fall towards the "valley" of bent space-time. It is also believed that these large objects tend to drag space-time around with them wherever they go. In other words, these massive objects are not only making a depression in space time, but they are also, in a sense, twisting the fabric all around themselves. Einstein was also able to prove that time was, in fact, not absolute. It has the ability to change and warp. With all this in mind, it was no longer an accepted idea to think of space as flat.[4]
Even Light is Effected by Gravity
Though one might think light would be able to escape the affects of gravity, it truely is not able too. Light is also affected by gravity just as everything else in the universe. Just as you might throw a ball into the air it will then lose energy the farther it goes. The same thing happens to light as it travels from its source though Electromagnetic waves do not lose energy by going a slower speed. Electromagnetic waves is the scientific name given to light. It achieves this by changing from say a blue frequency to a red frequency which is lower than blue. It is not that different from the way that sound might be changed from where you hear it. Like when an emergency vehicle passes and the pitch changes relative to the po
How it was discovered?
How Newton discovered universal gravitation was actually by accident. When he saw that apple fall it is thought he started to wonder that if gravity, as he called it, applies here on earth why shouldn’t it apply to everywhere else. He made this discovery in 1666 when he was only twenty four. That’s a big thing considering all the people of the time where more worried about catching the plague. Although he was enrolled in Cambridge university, at that point in time he was at home to avoid the plague, but that’s most of his greatest discoveries were made. It was almost twenty years later, though, when he finally published his findings on this and many other things, including his three laws. Only when Halley persuaded him did he finally publish his findings in the “Principia Mathematica Philosophiae Naturalis.” It is hard to say where we might be today in our knowledge of physics if he had not been sitting under that apple tree. Some of the other contributions Newton discovered durng this time would be things such as binomial theorem, differential calculus, rector addition, centripetal acceleration, and optics. That’s probably why they made him a professor right off when he finally returned to Cambridge after the plague had lifted.
Black Holes
Presentation
References